1. Field of the Invention
This invention relates to a process for producing a vinylidene fluoride resin, and more particularly to a process for producing with ease a vinylidene fluoride resin having a superior water repellency and having a controlled molecular weight.
2. Description of the Prior Art
Polyvinylidene fluoride is used in various fields because of its superior weatherability, corrosion resistance, electrical properties, processability and so forth. However, polyvinylidene fluoride has the disadvantage that its water repellency is a little inferior to fluoride resins of different types.
Accordingly, in order to improve the water repellency, it is necessary to produce a block copolymer of vinylidene fluoride with a fluorine-rich monomer such as hexafluoropropylene, tetrafluoroethylene or the like. For example, it is known to use a method of successive growth that is employed in the production of living polymers, a method of coupling at least two polymers, a method of subjecting terminal functional groups to polyaddition or polycondensation or a method of radical polymerization.
In these methods, however, the fluorine-rich monomer has a polymerization rate lower than that of the vinylidene fluoride monomer, so that the vinylidene fluoride monomer undergoes polymerization in preference to the fluorine-rich monomer to cause the problem that the fluorine-rich monomer is concentrically introduced into the terminal sites of the molecule. Further, there are problems such that homopolymers tend to be formed as by-products and the molecular weight of the resin can be controlled with difficulty. In particular, a copolymer with an excessively large molecular weight (e.g., a viscosity-average molecular weight of 500,000 or more) has so high a melt viscosity that its processability into films or the like is deteriorated.